a. Field of Invention
The invention relates generally to single screw extruders and multi-screw extruders, especially twin screw extruders that utilize gravity-filled plunger feeders to precisely control rate of feed to the extruders. In some preferred embodiments, the present invention devices are for batch preparation of small-scale products, such as pharma products, and extremely accurate feed rates and product densities are achieved using present invention device micro-plungers.
b. Description of Related Art
The following patents are representative of various types of extruders:
U.S. Pat. No. 7,229,205 B2 to Schunk et al. describes a drive unit for operating a plastics injection machine including a rotatably supported bushing intended for accommodation of an extruder screw and a rotor which includes a hollow shaft and is defined by an inner diameter sized to allow passage of the bushing and accommodated extruder screw through the rotor. The rotor is hereby detachably connected with the receiving member in fixed rotative engagement.
U.S. Pat. No. 7,168,944 B2 to Schad describes an energy efficient drive system provided for use on typical injection molding machines whereby a single electric motor drives both the extruder screw and a hydraulic motor that continuously charges a hydraulic accumulator during the extrusion process. During the injection cycle, the charge in the accumulator is directed to stroke the extruder screw and inject melt into the mold cavities. Another embodiment utilizes a similar arrangement on the clamp mechanism of the injection molding machine whereby the charge in the accumulator is directed to hold the mold closed during the injection cycle.
U.S. Pat. No. 6,481,043 B2 to Anderson et al. describes a rotary brush attachment tool for a hand-held vacuum cleaner having a dust bowl terminating in a nozzle end providing a mechanical force that acts to move foreign matter into the attachment tool from which the foreign matter is drawn into the nozzle end of the dust bowl of the hand-held vacuum cleaner to which it is removably attached.
U.S. Pat. No. 6,168,417 B1 to Takahashi describes a vertical molding machine vertically provided with a pre-plastication injection unit where an injection unit and a plastication unit are mounted side by side. The tips of these units are linked by a connecting pipe to transfer resin plasticated by the plastication unit to the injection unit therethrough. The injection unit and the plastication unit are individually supported by respective pairs of supports standing upright above a clamping device. The injection unit has an arm member on either side thereof and a spring member is provided on the top of the arm member. The plastication unit is held on the arm member through the spring member, where the supports for the plastication unit are inserted through the arm member and the spring member.
U.S. Pat. No. 6,086,353 to Klaus describes a two-stage, all-electric injection unit. More specifically, an injection unit in which the feed screw is preferably used only for plastication and the injection of the plasticized material is accomplished by a separate accumulator having an electrically driven linear actuator, such as a ball screw mechanism. The plunger of the accumulator is configured with a helical flight and is rotatable by way of a one-way clutch interposed between the plunger and the ball screw.
U.S. Pat. No. 5,863,567 to Klaus describes a two-stage, all-electric injection unit. More specifically, an injection unit in which the feed screw is preferably used only for plastication and the injection of the plasticized material is accomplished by a separate accumulator having an electrically driven linear actuator, such as a ball screw mechanism. The accumulator is configured so that the ratio of the piston stroke to the piston diameter is preferably in the range of ten to fifteen. In the preferred embodiment there are separate motors for rotation of the screw and operation of the accumulator. An alternate embodiment is disclosed wherein the system is driven with a single motor and one-way clutches.
U.S. Pat. No. 5,454,995 to Rusconi et al. describes a method of the present invention related to reducing cycle time in injection molding machines that are running large capacity molds, such as multiple cavity perform molds, and require a high volume supply of quality melt. Specifically, the present invention proposes using a continually plasticising extruder to supply two melt accumulators that will alternately operate to inject the plastic material into the mold. To accomplish this, a rotary valve at the end of the extruder is controlled to fill the pots, and ball check valves are positioned to control flow direction and limit pressure in certain parts of the system. A shuttle valve between the shot pots and before the nozzle facilitates decompression.
U.S. Pat. No. 5,281,384 to Banks describes an improved method for injection molding including the steps of plasticizing a shot of molding material with the extruder running at a high rpm, transferring the shot to an accumulator means with the extruder running at a low rpm, and injecting the shot into a mold cavity.
U.S. Pat. No. 4,512,730 to Kudert et al. describes a device for use with a runner block and a multipolymer co-injection nozzle having separate rear entrance ports for separate polymer streams, in a multicoinjection nozzle, multi-polymer injection molding machine, for receiving from the runner block a plurality of separate polymer flow streams and for redirecting them to flow axially out of the forward end of the device into the nozzle rear entrance ports. The device has inlets cut radially into its periphery, each for receiving a polymer flow stream, and has feed channels, each in communication with an inlet and having an inward portion cut toward the device's central axis, and an axial portion communicating with the inward portion, running axially forward and terminating at an exit hole in the device's forward end, the exit holes being in a spaced pattern for feeding the separate polymer flow streams in spaced relation into the nozzle rear entrance ports. In preferred embodiments, the inlets communicate with feed throats, each cut radially into and running about a portion of the circumference of the device and having a terminal end portion which communicates with an axial feed channel, and receiving chamber, desirably of stepped configuration, is cut axially into the forward end and adapted to receive a co-injection nozzle. Most of the exit holes are radially spaced from each other by an arc of 60°. Isolation means, preferably including a plurality of annular grooves are cut into the periphery of the device between inlets and have an expandable piston ring seated therein to maintain the polymer flow streams isolated from one another.
Notwithstanding the prior art, the present invention is neither taught nor rendered obvious thereby.